Art of coating metals with lead



March 13, 1934. D. D. JACK5ON ART OF COATING METALS WITH LEAD Filed May 5, 1932 Patented Mar. 13, 1934 UNITED STATES 1,950,612 ART OF COATING TMETALS WITH LEAD Daniel D. Jackson, Brooklyn, N. Y., assignor to American Machine and Foundry Company, New York, N. Y., a corporation of New Jersey Application May 3, 1932, Serial No. 609,008

6 Claims.

This invention relates to the art of coating metals, particularly to the coating of one metal vnth another for protection from corrosion. It has especial application to the coating of metals such as iron or steel with lead.

It is well known that it is very difiicult to apply a coating of lead to iron or steel in such a manner that the protective lead coating will adhere to the iron or steel in a covering sufliciently adherent and continuous to prevent corrosion and oxidation of the iron or steel. It is also well known that if a very small quantity of phosphorus is introduced into a bath of molten lead, a closely adherent continuous lead coating without pinholes or breaks through which corrosion or oxidation might take place, can be formed upon iron or steel.

But another problem is here presented. It is a matter of great difficulty to incorporate phosphorus with lead and, consequently, to introduce it into the molten lead bath.

Although previous methods for such introduction have been heretofore devised and have been satisfactory for use under certain conditions, they have left a good deal to be desired. It has been proposed to add a small percentage of phosphor tin, copper phosphide or other metal phosphides or other phosphorus compounds to the bath. This, however, is difficult, due to the fact that the melting point of these phosphides is considerably higher than that of lead and also to the fact that non-metallic phosphorus compounds or phosphorus itself are difiicult to introduce for the reason that the light weight of the metallic compounds of phosphorus as compared with lead causes them to float on top of the bath and, in the case of phosphorus itself, to burn off rapidly with little or no effect upon the molten lead.

It isan object of the present invention to provide a practical method of introducing phosphorus into a bath consisting substantially of lead, thereby rendering it' a suitable coating bath for iron or steel.

It is a further object to provide an apparatus adapted to introduce the phosphorus into the bath in a very eficient manner.

In preparing the bath, a known quantity of lead is melted and brought to a temperature of about 600 F. At this temperature about onehalf of one percent. of tin may be added and allowed to melt in the bath. The bath is then ready for the introduction of phosphorus.

The phosphorus may be introduced into the bath in any form but I prefer to use red phosphorus which will not take fire in the air at room temperatures and the vapors of which are not poisonous. Under the present invention, the phosphorus is introduced into the lead bath by means of an apparatus adapted to restrain and prolong its action. The apparatus used for introducing phosphorus forms an important feature of the'present invention. A suitable apparatus for this purpose is illustrated in Fig. 1 of the drawing; Fig. 2 illustrates how' the device of Fig. 1 may be satisfactorily utilized for the purposes of the present invention.

The apparatus of Fig. 1 consists of a capsule or metal tube 10, preferably of iron, which may be provided at its ends with screw-threads 11 on which caps 12 may be threaded. The caps may be provided withindentations 17 in their ends so that the capsule may be readily gripped by the means to be hereinafter described. The tube is perforated along its length, for instance, by perforations 13 and 14 at the top and bottom thereof. In the illustrative embodiment, the perforations 13 at the top of the tube are of a relatively large diameter, a quarter of an inch or larger, whereas the perforations 14 at the bottom are relatively small, say one sixty-fourth of an inch. The capsule or tube is then charged with phosphorus 16. r

I prefer to use for this purpose red phosphorus which is tightly packed into the capsule or tube the screw caps 12. As an additional precaution,

I may insert a strip of lead 15 inside the capsule over the openings before charging. This prevents the phosphorus from escaping from the capsule until the lead strip has melted from the heat of the bath. The purpose of this is to allow sufiicient time for the operator to put the capsule in place at the bottom of the bath and to get away before the fumes and flames begin to rise, which would happen instantaneously if the lead strip were not used. This protection, however, may be achieved by other means and I do not find it desirable in any case to use the lead strip except to cover the larger perforations which, as will be seen hereinafter, I usually place in an upward position in the bath.

Special means must be provided to force the capsule with its charge of phosphorus to the bottom of the bath, for if it were simply dropped into the bath it would float on the surface of the lead and the phosphorus would ignite and burn off with little or no beneficial effect upon the molten lead.

To this end I provide. a holder, such as a pair of tongs 18 of sufficient length to reach the bottom of the kettle 20 containing the coating bath 19, shown as molten lead with a layer of melted tin 22 floating thereon. The capsule, having been charged and closed, is grasped by the ends of the tongs and forced either manually or mechanically to the bottom of the kettle. In Fig. 2 I have illustrated tongs 18 adapted for manual operation, and whenthe capsule has been forced to the bottom of the kettle, the tongs are clamped to a standard 23 by. means of a suitable clamp 24. The standard 23 is arranged as desired; for instance, it is attached to the side of the kettle structure 21. As indicated inthe illustrative embodiment, the kettle comprises a refractory construction 21 in which is seated an ironcontainer 20. The kettle 20 may be provided with a hood (not shown) fitted with a suitable discharge opening, for the purpose of carrying away the ases.

Upon introduction of the capsuleinto the bath as above described, the lead strip begins to meltgivlng ample time to the operator properly to position and clamp it and getaway from the kettle before the fumes and flames startto arise. However, as soon as the lead strip has melted and the reaction starts, a very heavy churning effect takes place in the bath, the vaporized phosphorus boiling up through the lead and by this churning action effecting a very thorough mixing of the tin with the lead in the bath. Very vivid flames are given ofi. This vigorous action continues for a considerable time. If a capsule containing about 8 ounces of red phosphorus and measuring about six inches-long and about twolinches in diameter is used, the vigorous churning effect and vivid fiames last for about twenty minutes, after which the vigorous action subsides and a weaker churning and a more intermittent flaming continues over a very long period. Three such capsules of the dimensions specified and containing the amount of phosphorus indicated will activate as much as 12,000 pounds of lead if positioned in the kettle at suitable distances apart.

A bath of lead so activated is suitable for the coating of iron or steel materials whether in the form of sheet, wires, or shapes. Moreover, a quantity of lead once activated by the process of the present invention retains its coating properties indefinitely.

It is not essential to add any tin to the bath but a small quantity, say about one per cent., greatly improves the activation. As little as onehalf of one per cent., or even less, gives satisfactory results for certain purposes. More than this small quantity does not seem to improve the efiiciency or the coating range to any material extent. It is, however, desirable to add larger quantities of tin for some purposes, since it considerably brightens the coating and adds some degree of hardness thereto. It is difllcult for an unpraoticed eye to distinguish a coating consisting of 10% tin in lead prepared according to this invention, from a coating of pure tin.

The addition of tin to the lead bath before activation with phosphorus has, furthermore, another beneficial eifect. It is, as I have above pointed out, possible to coat iron or steel with lead without the addition of tin or other metals when the lead hasbeen activated in accordance with this invention. The temperature at which this may be done. is, however, very critical and must be maintained at about 800 to 825 F. But the addition of even one-half of one per cent. tin is sufficient to permit such-coating over a much wider range, as, for example, between about 600 and 800 F. Beyond this small addition, however, no important advantage is secured except in the appearance of the coating.

. The process may also be carried out by subatituting other metals than tin in the bath. Any

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other metal having an afiinity for phosphorus may be used. For example, a small quantity of copper maybe melted with the lead and an ex cellent coating metal will, be obtained.

The efiiciency of the molten bath as a coating bath is greatly improved by the thorough mixing of the tin in thelead which is due to the violent churning or ebullition of the molten metal by the phosphorus vapors rising from the bottom of the kettle through. the whole molten mass.

Furthermore, the molten metal, once it has been' activated in this manner, may be used either directly as a coating bath or it may be formed into ingots and kept in solid form for use as desired.

What I claim is: v

1, The method of coating metals comprising preparing a molten bath of lead, maintaining a quantity of phosphorus immersed therein while delaying the reaction between the lead and phosphorus and subsequently passing the metal to be coated through said bath. I

2. The method of preparing lead coating material for metals which comprises introducing phosphorus into a bath of molten leadand. at the bottom thereof, causing said phosphorus to vaporize and so controlling such vaporization as to permit only a slow and gradual release of phosphorus vapors through the molten lead.

, 3. The method of preparing lead coating material for metals which comprises preparing a melt of lead, melting therein tin, immersing a quantity of phosphorus at the bottom of said lead-tin melt and so controlling the phosphorus vapors as to .permit only a slow and gradual release of said amounts at a time rise through said melt.

5. A device for effecting the release of phosphorus vapors in a molten metal bath which comprises a container of a metal having a higher melting point than the metal composing the bath, adapted to hold phosphorus in solid form, said container having perforations so adapted and arranged as to size as to permit a slow escape of phosphorus vapors formed with said container, at least some of said perforationsbeing covered on the inside of the container with a shield of a metal having a melting point not exceeding that of the bath.

6. A container adapted to hold a charge of vaporizable solid material which consists of a capsule of a material having a melting point sumciently high to withstand the temperature conditions under which it is to be employed, said capsule having walls containing perforations graduated in size. so as to permit a slow escape of vapors formed within said capsule, at least some of said perforations being covered" on the inside of the container with a shield of a metal having a melting point not exceeding that of the bath.

DANIEL D. JACKSON.

CERTIFICATE or Connecticut Patent No. 1,950,612. March is, 1924.

mm JACKSON;

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as foiiows: Page 2, line 129. claim 5, Mr "with" read within; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Qffice.

Signed 'and sealed this 15th thy of May, A. D. 1934.

Bryan M. Battey (Seal) Acting Commissioner of Patents. 

